The present invention relates generally to apparatus for coating elongated objects in a hot dip galvanizing kettle and in particular to an automatic conveying mechanism for continuously feeding and removing such objects from the kettle.
Commonly used procedures in the industry for hot dip galvanizing elongated objects have often included one or more manually performed functions. For example, in feeding elongated objects and particularly pipe to a galvanizing kettle, the operator has manually fed the pipes to the molten zinc bath and then forced the same downwardly to keep the pipes from floating on the zinc or from improperly entering the same. After the pipes have been in the molten zinc for a period of time and have been moved from the entry to the exit side of the kettle by engagement with subsequently inserted pipes, it has been common practice for the operator to place a rod provided with an end hook into the molten zinc to grab one end of a submerged pipe and then to pull that end upwardly so that it can be engaged or tagged by a series of inclined magnetic rollers which are rotatably driven to effect withdrawal of the coated pipe from the bath.
In the above-described exemplary manual operations, the hot dip galvanizing procedure has many disadvantages from both manufacturing and marketing standpoints. Perhaps most importantly, the pipe sections being coated are not controlled during their submersion in the galvanizing bath which results in nonuniformity of coating thickness both as to the zinc layer and the zinc-iron alloy layer. Control in such manual operation is lost of course by the submerged pipes assuming a random orientation within the coating material, and such control is further lost by the random manual hooking of individual pipes for removal from the bath. Thus the pipe sections first inserted in the bath may well be among the last pipes removed therefrom because of the tendency of such first inserted pipes to assume a position at the bottom of the pile. As a result, the first inserted but last removed pipes have thicker zinc-iron alloy and zinc coat layers resulting in nonuniformity of the pipes coated, which does not permit the manufacturing operation optimally to be controlled in accordance with the end product application and also may result in field bending problems and the like. Also, the described manual operations require a greater labor input and cost compared to automatic or semi-automatic procedures.
Over the years, many different automatic or semi-automatic procedures have been developed in an attempt to eliminate one or more of the above-noted disadvantages in the manual feeding and drag out procedure. Such automatic or semi-automatic procedures can generally be classified in accordance with the structure used to move the pipe through the liquid metal bath as follows: (1) star wheels, sprockets, or combinations thereof; (2) pivotally or axially movable arms; (3) endless chain; and (4) screw conveyors.
Referring initially to the star wheel conveying approach, Cunningham U.S. Pat. No. 1,521,010 is fairly representative of the structure employed in such approach. More specifically, such patent discloses two longitudinally spaced star wheels keyed to a rotatable shaft, such star wheels having notches to receive and engage spaced apart sections of a pipe extending therebetween. Upon rotation of the shaft, the star wheels convey the engaged pipe through a coating bath to a removal platform. The star wheel approach has limited production capabilities due to the limited number of notches that can be formed in the circumferential periphery of wheels having operative diametrical dimensions. Reference may also be made to Townsend U.S. Pat. 2,701,546 for a similar star wheel teaching.
Referring now to the second approach and specifically Church U.S. Pat. No. 2,184,610, an automatic feeding device is disclosed which includes a rack and pinion pusher arm which is forwardly indexed to engage the leading pipe on the feed table forcibly to submerge such pipe in the molten metal bath. The pusher arm is then rearwardly indexed to repeat the reciprocating cycle which results in the pipe submersion being a function of pipe-to-pipe engagement rather than positive mechanical control. Church teaches operator removal of the submerged pipe by hooking one end for tagging to a magnetic roller, which teaching again requires manual random hooking of pipe sections below the surface of the zinc.
Referring now to the third approach, Elliott U.S. Pat. No. 3,340,850 discloses an apparatus continuously for conveying tubes through a hot galvanizing bath which includes two vertically oriented but longitudinally spaced endless chain conveyors having outwardly extending arms each of which receive a group or bundle of hollow elongated tubes. The ends of the tubes thus conveyed are received in J slots to assist in guiding the same during movement through the zinc material. The structure disclosed in the Elliott patent does permit a first in, first out feeding sequence but is subject to operational disadvantages. More specifically, the conveying mechanism disclosed in Elliott depends upon relative movement between parts and specifically the freedom of pivotal movement between adjacent chain links. However, during discontinuities or shutdowns in operation, the structure disclosed in the Elliott patent has the tendency to "freeze up", that is, the zinc contacting the chain links solidifies and thus precludes or reduces the freedom of relative mechanical movement required.
The fourth approach then to the manual feed and drag out technique described above is disclosed for example in Free U.S. Pat. No. 1,935,087. Free teaches a horizontally oriented conveying mechanism adapted to deliver pipe sections to one diametrical side of three angularly inclined and longitudinally spaced screw feeds for driving the pipes into a molten zinc reservoir. Free discloses two different embodiments for removal of the submerged pipe. As shown in FIG. 3, a hook mechanism on the bottom of an elongated rod can be used to support two pipe sections with such hooks being reciprocally vertically cycled for raising the corresponding ends of the two pipe sections for removal by a conveying mechanism. Alternatively as shown in FIGS. 5A and 6A, a single inclined removal screw is used at one end of the bath cooperatively to receive pipe sections dropping off of the three angularly inclined screw feeds. However, in both embodiments of the Free patent, control is momentarily lost over the pipe sections as transfer is effected between the initial feeding mechanism and the withdrawal or removal mechanism. In some instances, this momentary loss of control may create operational problems in that the pipe sections are either left at the bottom of the reservoir requiring subsequent hand removal or the desired first in, first out control is lost. Reference may also be made to Faugeras U.S. Pat. No. 3,382,046, which discloses separate feed and removal conveyors similar to the Free patent but in a different and unrelated decanning environment.
Still another screw type conveying system approach for hot dip galvanizing is disclosed in Turner U.S. Pat. No. 3,063,409 wherein two cone type conveying screws having threads of increasing diameter are disclosed for submerging the pipe sections in the galvanizing bath. Once such pipes are submerged, the Turner patent discloses release by the screws for transverse removal of the pipe sections through a cooperative camming and magnetic roller withdrawal system. Thus again there is a transfer of control from one mechanism to another within the liquid molten metal.
The principal object of the present invention is to provide a conveying mechanism that retains control of the elongated objects throughout their entire movement through the hot dip galvanizing kettle. Such control, which is effected by simultaneously and synchronously driven U-shape screws, permits a first in, first out object feeding and drag out sequence to be obtained. Moreover, the variable speed drive for such U-shape screws likewise permits control over the immersion time for the elongated objects which results in the ability to control the thickness of the zinc-iron alloy and zinc layers.
It is another object of the present invention to provide apparatus for increasing the relative elongated object feed rate for the coating procedure while maintaining the necessary control. Such object is accomplished by coordinating feed and drag out structure to the advantages provided by the novel U-shape screw conveying structure. More specifically, at the feed side of the screws, structure is provided to place elongated objects on opposed diametrical sides of the screws, thereby to double the capacity of the same. Such result may be accomplished by any form of initial conveying mechanism operative to position pipe sections on both diametrical sides of the U-shape screws. On the drag out side of the screws, removal of the coated elongated objects is initiated by two vertically staggered magnetic rolls which are operative simultaneously to tag the two staggered pipes at opposite sides of the screws, thereby to coordinate the drag out removal rate to the feed rate.
Still another object of the present invention is to provide U-shape screws that are operative automatically to move the objects in controlled fashion from a feed conveyor, through the bath, to a series of removal rollers without any intervening transfer structure being required.
It is yet another object of the present invention to provide U-shape screws having variably pitched threads at both the entrance and exit sides of the bath automatically to tilt hollow objects such as pipe for insertion into the bath and removal from the bath. Such tilting upon entry permits the zinc to move through the hollow pipe from one end to the other thus precluding the formation of intermediate air bubbles which may result when zinc enters both ends of a horizontally inserted pipe. Upon removal, the tilting of the pipes permits the excess zinc on the inside and outside surface of the pipe freely to run downwardly back into the molten metal bath.
Other objects and advantages of the present invention will become apparent as the following description proceeds.
To the accomplishment of the foregoing and related ends the invention, then, comprises the features hereinafter fully described and particularly pointed out in the claims, the following description and the annexed drawings setting forth in detail certain illustrative embodiments of the invention, these being indicative, however, of but a few of the various ways in which the principle of the invention may be employed.